Millable bridge plug system

ABSTRACT

A millable bridge plug system includes a mandrel, a sealing member, ring members, cone assemblies, and slip devices. The sealing member, ring members, cone assemblies and slip devices are positioned on and around the mandrel. Ring members push against an upper end and lower end of the sealing member. The sealing member has a surface interface contacting each of the ring members so that pressure from the ring members is exerted according to contact along the surface interface. The surface interface can have a curvature or be a double radiused surface. The ring members are pushed against the cone assemblies, and the ring members have ring surface interfaces contacting the cone assemblies. The pressure from the cone assemblies is exerted according to contact along the ring surface interface of the ring members. Coordination of the surface interfaces and ring surface interfaces control pressure to insure improved sealing against the wellbore.

RELATED U.S. APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO MICROFICHE APPENDIX

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a downhole tool for isolating zones in a wellbore. More particularly, the present invention relates to a millable bridge plug system.

2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.

A bridge plug is a downhole tool that is lowered into a wellbore. At a particular distance through the wellbore, the bridge plug is activated. The bridge plug locks and opens to seal the bridge plug to the walls of the wellbore. The bridge plug separates the wellbore into two sides. The upper portion can be cemented and tested, separate from the sealed lower portion of the wellbore. Sometimes the bridge plugs are permanent, and they seal an entire portion of the wellbore. Other times, the bridge plugs must be removed, and still other times, the bridge plugs must be removed and retrieved. These removable bridge plugs are millable or drillable, so that a drill string can grind through the bridge plug, making remnants of the destroyed bridge plug to remain at the bottom of a wellbore or to be retrieved to the surface by drilling mud flow.

Bridge plugs generally include a mandrel, a sealing member placed around the mandrel, ring members adjacent the end of the sealing member and around the mandrel, upper and lower slip devices at opposite ends of the mandrel, and respective upper and lower cone assemblies engaged to the upper and lower slip devices. FIG. 1A shows the prior art bridge plug system 10 with a mandrel 12, sealing member 14, and upper and lower slip devices 16 and 18 shown. The bridge plug is placed in the wellbore by a setting tool on a positioning assembly, such as wireline, coiled tubing or even the drill string itself. Once in position at the correct depth and orientation, the bridge plug is activated. The setting tool holds the mandrel 12 in place, while a ramming portion of the setting tool exerts pressure on the stack, which includes the sealing member 14 and the slip devices 16 and 18. The end 22 has a cap which prevents the stack from sliding off the mandrel 12, when the ramming portion of the setting tool hits the stack. Instead, the pressure of the ramming portion compresses the stack, forcing the sealing member 14 to radially extend outward to seal against the wellbore or case and to flatten to a smaller height along the mandrel. The slip devices 16 are toothed and are distended radially outward by the stack to dig into the wellbore walls, locking the sealed configuration of the stack. The lower slip device 18 holds position by the cap at the end 22, while the upper slip device 16 lowers and locks the seal of the spread sealing member 14. When the ramming portion has compressed and locked the stack, the end 20 proximal to the setting tool on the positioning assembly is sheared, separating the bridge plug from the setting tool and the positioning assembly. FIG. 1B shows the prior art bridge plug system 10 in an activated and set state. Pressure on the lower cone assembly against the lower slip device 18 at the distal end of the mandrel causes the lower slip device 16 to open and latch against the wellbore. Continuing pressure by the ram expands the sealing member 14 against the rings to form a seal against the walls of the wellbore. Pressure on the upper cone assembly causes the upper slip device 18 to also open and latch against the wellbore, setting the seal of the sealing member.

The activation of the bridge plug requires advancement for a more efficient and stable seal in the wellbore. The ramming portion provide the force needed to form the seal on the wellbore, and this force is directed by those stack structures, the sealing member, ring members, cone assemblies, and slip devices, of the bridge plug. The interactions between these stack structures are important for efficiency and consistency of the forming the seal and locking the seal on the wellbore. The pressure is exerted directly on the sealing member by ring members in some arrangements of the stack structures. The interface between the sealing member and the ring members of the prior art has a constant taper angle between the sealing member and the ring members. The amount of pressure against the sealing member does not vary as the pressure of the positioning assembly is exerted through the ring members. The expansion of the sealing member to the wall of the wellbore is steady, yet possibly insufficient for an adequate seal. The lack of a threshold amount of pressure for setting the seal may result in a sealing member that is not expanded enough to form a good seal or extrusion of the sealing member beyond the ring members due to too much pressure. The exerted pressure on the sealing member may also be too much, causing extrusion and degradation of the seal member. There is a need for resistance to excess pressure after the seal is formed.

Conventional materials of the millable bridge plug, like all downhole tools, must withstand the range of wellbore conditions, including high temperatures and/or high pressures. High temperatures are generally defined as downhole temperatures generally in the range of 200-450 degrees F.; and high pressures are generally defined as downhole pressures in the range of 7,500-15,000 psi. Other conditions include pH environments, generally ranging from less than 6.0 or more than 8.0. Conventional sealing elements have evolved to withstand these wellbore conditions so as to maintain effective seals and resist degradation.

Metallic components have the durability to withstand the wellbore conditions, including high temperatures and high pressures. However, these metallic components are difficult to remove. De-activating and retrieving the bridge plug to the surface is costly and complicated. Milling metallic components takes time, and there is a substantial risk of requiring multiple drilling elements due to the metallic components wearing or damaging a drilling element of a removal assembly.

Non-metallic components are substituted for metallic components as often as possible to avoid having so much metal to be milled for removal of the bridge plug. However, these non-metallic components still must effectively seal an annulus at high temperatures and high pressures. Composite materials are known to be used to make non-metallic components of the bridge plug. These composite materials combine constituent materials to form a composite material with physical properties of each composite material. For example, a polymer or epoxy can be reinforced by a continuous fiber such as glass, carbon, or aramid. The polymer is easily millable and withstands the wellbore conditions, while the fibers also withstand the wellbore conditions and resist degradation. Resin-coated glass is another known composite material with downhole tool applications. Composite materials have different constituent materials and different ways of combining constituent materials.

It is an object of the present invention to provide an embodiment of a millable bridge plug system.

It is another object of the present invention to provide an embodiment of the millable bridge plug system with improved stack structures, including a sealing means.

It is still another object of the present invention to provide an embodiment of the millable bridge plug system with a sealing means with controlled deformation by pressure.

It is yet another object of the present invention to provide an embodiment of the millable bridge plug system with a sealing means having an active surface interface with respective ring members.

It is another object of the present invention to provide an embodiment of the millable bridge plug system with improved ring members.

It is still another object of the present invention to provide an embodiment of the millable bridge plug system with ring members with an active ring surface interface with cone assemblies.

These and other objectives and advantages of the present invention will become apparent from a reading of the attached specifications and appended claims.

SUMMARY OF THE INVENTION

A millable bridge plug system comprises a mandrel, a sealing means positioned around the mandrel, a plurality of ring members, a plurality of cone assemblies, and a plurality of slip devices. The sealing means has an upper end and a lower end. A first ring member is placed adjacent the upper end of the sealing means, and a second ring member is adjacent the lower end of the sealing means. A first cone assembly is proximate to the first ring member, and a second cone assembly is proximate to the second ring member. The slip means extend radially outward and engage an inner surface of a surrounding borehole to lock the position of the bridge plug. A first slip means is mounted around the mandrel and engages the first cone assembly, and a second slip means is mounted around the mandrel and engages the second cone assembly.

The sealing means further comprises a first means for resisting pressure by the first ring member when in contact with the first ring member, and a second means for resisting pressure by the second ring member when in contact with the second ring member. The first means is on the upper end and the second means is on the lower end. In one embodiment, the first and second means for resisting pressure are comprised of surface interfaces with curvatures. In another embodiment, the first and second means for resisting pressure are comprised of double radiused surfaces. When pressures are exerted by the ring members on the upper end and the lower end of the sealing means, the sealing means is deformed to spread radially towards the borehole at a rate dependent upon location of the pressures on the curvatures of the surface interfaces or the double radiused surfaces. The sealing means also has an inner cavity curved from the upper end and the lower end towards an indentation in a middle of the sealing means.

The first ring member may also have a first ring means to resist pressure when in contact with the first cone assembly, and the second ring member may also have a second ring means to resist pressure when in contact with the second cone assembly. Similar to the first and second means for resisting pressure, the first and second ring means for resisting pressure are comprised of ring surface interfaces with ring curvatures. Alternatively, the first and second ring means for resisting pressure are comprised of single radiused surfaces. When pressures are exerted by the cone assemblies on the ring members, the ring members are deformed and pass pressure through to the sealing means at a rate dependent upon location of the pressures on the curvatures of the surface interfaces or the single radiused surfaces.

The method of installing a millable bridge plug system comprises the steps of: placing a bridge plug in a wellbore, the wellbore having inner walls surrounding the bridge plug, forming a seal against the inner walls by exerting pressure on the bridge plug, and fixing position of the bridge plug by exerting additional pressure on the bridge plug. The bridge plug includes a mandrel having an upper portion and a lower portion, a sealing means positioned around the mandrel, a plurality of ring members, a plurality of cone assemblies, and a plurality of slip means for extending radially outward and engaging the inner walls. The step of forming a seal involves the sealing member being compressed to radially extend outward to seal against the inner walls, the ring members pushing the sealing member to expand, the cone assemblies pushing the ring members. The step of fixing position of the bridge plug involves the cone assemblies pushing the slip means to extend radially outward to fixedly engage the inner walls. The sealing means and the ring means can have means for resisting pressure so that the compression is controlled according to the means for resisting. The means for resisting can be surface interfaces with curvatures or single or double radiused surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic view of a prior art bridge plug system, being placed in a wellbore.

FIG. 1B is another schematic view of the prior art bridge plug system, being locked in position within the wellbore.

FIG. 2 is a perspective view of an embodiment of the bridge plug of the present invention.

FIG. 3 is an exploded perspective view of the embodiment of FIG. 2.

FIG. 4 is a cross-sectional view of an embodiment of the bridge plug of the present invention along an axis of the bridge plug, showing placement in the wellbore.

FIG. 5 is a cross-sectional view of an embodiment of the bridge plug of the present invention along an axis of the bridge plug, showing an activated configuration in the wellbore.

FIG. 6 is an isolated cross-sectional view of a sealing member and ring members of an embodiment of the bridge plug of the present invention.

FIG. 7 is an isolated perspective view of the sealing member and ring members of an embodiment of the bridge plug of the present invention as shown in FIG. 6.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 2-5, an embodiment of the millable bridge plug system 100 of the present invention is shown. The system 100 includes a mandrel 112, a sealing means 114, and a plurality of ring members, 116, 118, a plurality of cone assemblies 120, 122, and a plurality of slip means 124, 126. The sealing means 114, ring members 116, 118, cone assemblies 120, 122 and the slip means 124, 126 are stack structures mounted on the mandrel 112, sharing a common radial axis of alignment. FIGS. 2-5 also show a shearing means 128 and a cap means 130. The millable bridge plug system 100 is placed within a wellbore or borehole of a well by a setting tool. The wellbore or the borehole could have a casing or not, and the orientation of the wellbore is variable. FIG. 4 shows an embodiment with a casing 132. The bridge plug system 100 can be used in all ranges from generally vertical to generally horizontal orientations. As previously described, the millable bridge plug system 100 is used to isolate zones within the wellbore, separating sections of the wellbore for production or isolation. The system 100 is millable or drillable, such that a removal assembly, such as a drill string, can be used to grind through the system 100. All of the components of the system 100 are destroyed so that the isolated zone of the wellbore is removed.

The mandrel 112 of the system 100 is a generally tubular member formed of a material to withstand the heat and pressure of the borehole conditions. The mandrel 112 is also millable. The mandrel 112 may have a bridge 134, which seals the zone above the system 100 from the zone below the system 100. The sealing means 114 is positioned around the mandrel 112. The sealing means 114 has an upper end 136 and lower end 138 as shown in FIGS. 4 and 5. The sealing means 114 is generally symmetrical to start and is comprised of a deformable material.

FIGS. 2-5 also show the plurality of ring members, 116, 118. There is a first ring member 116 adjacent the upper end 136 of the sealing means 114 and a second ring member 118 adjacent the lower end 138 of the sealing means 114. The ring members 116, 118 surround the sealing means 114 and surround the mandrel 112. The ring members 116, 118 contact the sealing means 114 and can exert pressure on the sealing means 114. In an activated state, the system 100 has the sealing means 114 compressed to radially extend to contact the wellbore or casing 132. The ring members 116, 118 directly contact the sealing means 114. The seal created by the sealing means 114 isolates the zones on the wellbore. In combination with the bridge 130 in the mandrel 112, the wellbore is separated.

The system 100 also includes the plurality of cone assemblies, 120, 122. FIGS. 2-5 show a first cone assembly 120 proximate to the first ring member 116 and a second cone assembly 122 proximate to the second ring member 118. As shown in exploded view of FIG. 3, the first ring member 116 is mounted on the mandrel 112 between the first cone assembly 120 and the sealing means 114. Similarly, the second ring member 118 is mounted on the mandrel 112 between the second cone assembly 122 and the sealing means 114. The cone assemblies 120, 122 contact the ring members 116, 118 and can exert pressure on the ring members 116, 18. In an activated state, the system 100 has pressure of the cone assemblies 120, 122 pushing through the ring members 116, 118 to the sealing means 114.

FIGS. 2-5 also show the plurality of slip means 124, 126 for extending radially outward and engaging an inner surface of a surrounding borehole. The slip means 124, 126 lock the position of the system 100 by fixedly engaging the casing 132 or other structure on the inner surface of the borehole. The slips dig into the casing 132 to anchor the millable bridge plug system 100. Additional pressure can be exerted on the system 100 to create the seal with the sealing means 114, once the slip means 124, 126 are active or while the slip means 124, 126 are being activated. There is a first slip means 124 mounted around the mandrel 112 and engaging the first cone assembly 120 and a second slip means 126 mounted around the mandrel 112 and engaging the second cone assembly 122. The present invention may include further stack structures, such as cone seats, retainer rings or other supplemental ring members. Embodiments of the present invention relate to the structures and interactions between particularly defined stack structures to properly control the force exerted by the setting tool during installation.

FIGS. 6 and 7 show detailed views of the sealing means 114 and the ring members 116, 118 in an embodiment of the present invention. The upper end 136 of the sealing means 114 has a first means 140 for resisting pressure by the first ring member 116 when in contact with the first ring member 116. The lower end 138 of the sealing means 114 has a second means 142 for resisting pressure by the second ring member 118 when in contact with the second ring member 118. In one embodiment, the first means 140 for resisting pressure is comprised of a surface interface with a curvature, and the second means 142 for resisting pressure is also comprised of a surface interface with a curvature. The pressures exerted by the ring members 116, 118 on the upper end 136 and the lower end 138 of the sealing means 114 cause deformation of the sealing means 114 related to the first means 140 and the second means 142. The deformation of the sealing means 114 allows a greater surface area of the sealing means 114 to seal against the wellbore. There is a more even spread of the sealing member 114. A portion of the ring members 116, 118 may also spread to the wellbore for additional seal.

The rate of deformation is controlled by the location of the pressures on curvatures of the surface interfaces of the upper end 136 and the lower end 138 of the sealing means 114. The ring members 116, 118 do not provide steady or even pressure on the sealing member 114 to deform at a constant rate. Because of the curvature, the pressure along the curvature can build until a fulcrum is reached, wherein the tangential pressure to the curvature is sufficient to start the deformation of the sealing member 114. The present invention reduces the risk of insufficient pressure to deform the sealing member 114, causing extrusion instead of a seal on the wellbore. In prior art systems, the amount of pressure may be a gradual conical taper. The control of the pressure on the sealing member 114 cannot be controlled. A threshold of pressure at the fulcrum on the curvature of the present invention improves the seal formed on the inner walls of the borehole or casing 130. There is more surface area on the means for resisting pressure 140, 142 than the conventional tapers, wedges and conical surfaces. More even spread of the sealing member 114 can be achieved with embodiments of the present invention.

In an alternate embodiment, the first means 140 for resisting pressure is comprised of a double radiused surface with a curvature and double curvature, as shown in FIG. 6. The second means 142 for resisting pressure is also comprised of a double radiused surface in FIG. 6. Each double radiused surface has a fulcrum along the curvature to set the threshold to deform the sealing member and a smaller fulcrum further along the double curvature to resist further pressure and extrusion. The double radiused surface similarly controls the deformation of the sealing means 114 dependent upon location of the pressures on the double radiused surfaces of the upper end 136 and the lower end 138 of the sealing means 114 by the ring members 116, 118. The double radiused surfaces can reduce risk of extrusion and pressing too hard on the sealing member 114, which cannot be achieved with the wedges and other prior art structures.

FIGS. 6-7 also show the ring members 116, 118, which are contacted and pressed by the cone assemblies 120, 122. The pressures by the setting tool exerted through the cone assemblies 120, 122 deform the ring members 116, 118 and pass through to the sealing means 114. As shown in the views, the first ring member 116 has a first ring means 144 to resist pressure when in contact with the first cone assembly 120, and the second ring member 118 has a second ring means 146 to resist pressure when in contact with the second cone assembly 122.

The first ring means 144 for resisting pressure is comprised of a ring surface interface with a ring curvature, and the second ring means 146 for resisting pressure is comprised of a ring surface interface with a ring curvature. Pressures exerted by the cone assemblies 120, 122 on the ring members 116, 118 cause deformations of the ring members 116, 118 and affect the amount of pressure passed through to the sealing means 114, which forms the actual seal to the wellbore. The ring surface interfaces with ring curvatures control the deformation of the ring members 116, 118 and the amount of pressure passed through to the sealing means 114. Because of the ring curvatures, the pressure along each ring curvature can also build until a fulcrum is reached, wherein the tangential pressure to the ring curvature is sufficient to start the deformation of the ring members 116, 118 and pass pressure through to the sealing means 114. The ring curvatures of the first ring means 144 and the second ring means 146 prevent extrusion by controlling the amount of pressure passed through to the sealing means 114. The sealing means 114 is protected from too much pressure. Pressure builds to the fulcrum of the ring curvatures to finally release pressure to the sealing means 114. The first and second ring means 144, 146 are structures that may also extend radially to further seal against the wellbore.

In combination with the first means 140, the second means 142 on the sealing means 114 and the first ring means 144 and the second ring means 146 on the ring members 116, 118, the present invention controls pressure and reduces the risk of insufficient pressure to deform the sealing member 114, causing extrusion instead of a seal on the wellbore. These structures of the stack structures have interactions and interrelationships not present in the prior art. In prior art systems, the amount of pressure may be a gradual conical taper. The control of the pressure on the sealing member 114 cannot be controlled as disclosed by the present invention. FIGS. 6 and 7 show an alternate embodiment of the first ring means 144 and the second ring means 146 as single radiused surfaces. The shape of the single radiused surface similarly creates the fulcrum along the ring curvature of the other embodiment. The single radiused surfaces similarly control the deformation of the ring members 116, 118 and the amount of pressure passed through to the sealing means 114.

FIGS. 2-7, particularly FIG. 6, also show embodiments of the sealing means 114 with an inner cavity 148 with an indentation 150 between the upper end 136 and the lower end 138. The inner cavity 148 is curved from the upper end 136 to the indentation 150 and from the lower end 138 to the indentation 150. The sealing means 114 of the present invention further enhances the control of the deformation of the sealing means 114 to form the seal on the inner walls of the wellbore. The shape of the sealing means 114 allows more of the sealing member to radially extend and seal against the wellbore. The seal is more controlled and consistent, when the sealing member 114 is compressed from this shape by the ring members 116, 118 of the present invention. The pressure is centered through the width of the sealing member instead of being pinched at the wedge tip of a converging taper or cone. The ring members may also seal against the wellbore for an overall broader seal against the walls of the wellbore.

The method of installing a millable bridge plug system 100 comprises the steps of placing a bridge plug system 100 in a wellbore, forming the seal on the wellbore, and locking the system 100 in position within the wellbore. With the millable bridge plug system 100 of the present invention, system 100 is lowered into the wellbore having inner walls, such as a casing 130, using a setting tool on a positioning assembly. The mandrel is held in place as the stack structures 114, 116, 118, 120, 122, 124, and 126 are hammered by a ram portion of the setting tool. Pressure on the bridge plug system 110 forms a seal, when the sealing means 114 is compressed to radially extend outward to seal against the inner walls of the borehole. The ring members 116, 118 push the sealing means 114 to expand, and the cone assemblies 120, 122 push the ring members 116, 118. The cone assemblies 120, 122 also push the slip means 124, 126 to extend radially outward to fixedly engage the inner walls, locking the system 100 in position within the wellbore. At least one slip means 124, 126 is activated, so that stack structures are locked in the sealed position. The exerted pressure through the system 100 is controlled by the first means 140 and second means 142 on the sealing means 114, and sometimes in conjunction with the first ring means 144 and the second ring means 146 on the ring members 116, 118.

The present invention provides an embodiment of the millable bridge plug system with an innovative sealing means. The sealing means has a controlled deformation to create the seal under more known and predictable conditions, resulting in a more consistent and stronger seal. The pressure exerted on the millable bridge plug is more regulated by active surface interfaces and curvatures, including a double radiused surface in one embodiment. The improved control of the deformation is further facilitated by active ring surface interfaces and ring curvatures on the ring members.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated structures, construction and method can be made without departing from the true spirit of the invention. 

I claim:
 1. A millable bridge plug system, comprising: a mandrel; a sealing means positioned around the mandrel; a plurality of ring members, a first ring member adjacent an upper end of said sealing means and a second ring member adjacent a lower end of said sealing means, wherein said upper end of said sealing means has a first means for resisting pressure by said first ring member when in contact with said first ring member, and wherein said lower end of said sealing means has a second means for resisting pressure by said second ring member when in contact with said second ring member; a plurality of cone assemblies, a first cone assembly proximate to said first ring member and a second cone assembly proximate to said second ring member, said first ring member being between said first cone assembly and said sealing means, said second ring member being between said second cone assembly and said sealing means; and a plurality of slip means for extending radially outward and engaging an inner surface of a surrounding borehole, a first slip means mounted around said mandrel and engaging said first cone assembly and a second slip means mounted around said mandrel and engaging said second cone assembly.
 2. The bridge plug system according to claim 1, wherein said first means for resisting pressure is comprised of a surface interface with a curvature, and wherein said second means for resisting pressure is comprised of a surface interface with a curvature.
 3. The bridge plug system according to claim 2, wherein pressures are exerted by said ring members on said upper end and said lower end of said sealing means.
 4. The bridge plug system according to claim 3, wherein deformation of said sealing means is dependent upon location of said pressures on curvatures of the surface interfaces of said upper end and said lower end of said sealing means.
 5. The bridge plug system according to claim 1, wherein said first means for resisting pressure is comprised of a double radiused surface, and wherein said second means for resisting pressure is comprised of a double radiused surface.
 6. The bridge plug system according to claim 5, wherein pressures are exerted by said ring members on said upper end and said lower end of said sealing means, and wherein deformation of said sealing means is dependent upon location of said pressures on the double radiused surfaces of said upper end and said lower end of said sealing means
 7. The bridge plug system according to claim 1, wherein said first ring member has a first ring means to resist pressure when in contact with said first cone assembly, and wherein said second ring member has a second ring means to resist pressure when in contact with said second cone assembly.
 8. The bridge plug system according to claim 7, wherein said first ring means for resisting pressure is comprised of a ring surface interface with a ring curvature, and wherein said second ring means for resisting pressure is comprised of a ring surface interface with a ring curvature.
 9. The bridge plug system according to claim 8, wherein pressures are exerted by said cone assemblies on said ring members, wherein deformation of said ring members is dependent upon location of pressures on the ring surface interfaces by said cone assemblies, and wherein pressure exerted by said ring members on said upper end and said lower end of said sealing means is dependent upon location of said pressures on first and second means for resisting pressure of said sealing means and location of pressures on the ring surface interfaces by said cone assemblies.
 10. The bridge plug system according to claim 7, wherein said first ring means for resisting pressure is comprised of a single radiused surface, and wherein said second ring means for resisting pressure is comprised of a single radiused surface.
 11. The bridge plug system according to claim 10, wherein pressures are exerted by said cone assemblies on said ring members, wherein deformation of said ring members is dependent upon location of pressures on single radiused surfaces of said ring members, and wherein pressure exerted by said ring members on said upper end and said lower end of said sealing means is dependent upon location of said pressures on the first and second means for resisting pressure of said sealing means and location of pressures on the single radiused surfaces by said cone assemblies.
 12. A millable bridge plug system, comprising: a mandrel; a sealing means positioned around the mandrel; a plurality of ring members, a first ring member adjacent an upper end of said sealing means and a second ring member adjacent a lower end of said sealing means, wherein said upper end of said sealing means has a double radiused surface in contact with said first ring member, and wherein said lower end of said sealing means has a double radiused surface in contact with said second ring member; a plurality of cone assemblies, a first cone assembly proximate to said first ring member and a second cone assembly proximate to said second ring member, said first ring member being between said first cone assembly and said sealing means, said second ring member being between said second cone assembly and said sealing means; and a plurality of slip means for extending radially outward and engaging an inner surface of a surrounding borehole, a first slip means mounted around said mandrel and engaging said first cone assembly and a second slip means mounted around said mandrel and engaging said second cone assembly.
 13. The bridge plug system according to claim 12, wherein said first ring member has a single radiused surface in contact with said first cone assembly, and wherein said second ring member has a single radiused surface in contact with said second cone assembly.
 14. The bridge plug system according to claim 13, wherein said first ring member has a single radiused surface in contact with said upper end of said sealing means, and wherein said second ring member has a single radiused surface in contact with said lower end of said sealing means.
 15. The bridge plug system according to claim 14, wherein said single radiused surface of said first ring member engages said double radiused surface of said upper end, and wherein said single radiused surface of said second ring member engages said double radiused surface of said lower end.
 16. The bridge plug system according to claim 13, wherein said sealing means has an inner cavity with an indentation between said upper end and said lower end.
 17. The bridge plug system according to claim 16, wherein said inner cavity is curved from said upper end to said indentation and from said lower end to said indentation.
 18. A method of installing a millable bridge plug system, comprising the steps of: placing a bridge plug in a wellbore, said wellbore having inner walls surrounding said bridge plug, said bridge plug comprising: a mandrel having an upper portion and a lower portion; a sealing means positioned around the mandrel; a plurality of ring members, a first ring member adjacent an upper end of said sealing means and a second ring member adjacent a lower end of said sealing means, wherein said upper end of said sealing means has a first means for resisting pressure when in contact with said first ring member, and wherein said lower end of said sealing means has a second means for resisting pressure when in contact with said second ring member; a plurality of cone assemblies, a first cone assembly proximate to said first ring member and a second cone assembly proximate to said second ring member, said first ring member being between said first cone assembly and said sealing means, said second ring member being between said second cone assembly and said sealing means; and a plurality of slip means for extending radially outward and engaging said inner walls, a first slip means mounted around said mandrel and engaging said first cone assembly and a second slip means mounted around said mandrel and engaging said second cone assembly; forming a seal by exerting pressure on said bridge plug, said sealing member being compressed to radially extend outward to seal against said inner walls, said ring members pushing said sealing member to expand, said cone assemblies pushing said ring members; and locking said bridge plug within said wellbore by exerting pressure, said cone assemblies pushing said slip means to extend radially outward to fixedly engage said inner walls, said bridge plug being locked in position within said wellbore.
 19. The bridge plug system according to claim 18, wherein said first means for resisting pressure is comprised of a double radiused surface, wherein said second means for resisting pressure is comprised of a double radiused surface, wherein pressures are exerted by said ring members on said upper end and said lower end of said sealing means, and wherein deformation of said sealing means is dependent upon location of said pressures on the double radiused surfaces of said upper end and said lower end of said sealing means.
 20. The bridge plug system according to claim 18, wherein said first means for resisting pressure is comprised of a surface interface with a curvature, wherein said second means for resisting pressure is comprised of a surface interface with a curvature, wherein pressures are exerted by said ring members on said upper end and said lower end of said sealing means, and wherein deformation of said sealing means is dependent upon location of said pressures on the curvatures of said upper end and said lower end of said sealing means. 